JP6087108B2 - Cathode sorting method - Google Patents

Description

  The present invention relates to a cathode selection method, for example, a method for selecting a cathode of a beam source used in a charged particle beam drawing apparatus.

  In the electron beam apparatus, an electron gun serving as a beam source is used. There are various types of electron beam apparatuses such as an electron beam drawing apparatus and an electron microscope. For example, when it comes to electron beam drawing, it has an essentially excellent resolution and is used for the production of high-precision original picture patterns.

  Lithography technology, which is responsible for the progress of miniaturization of semiconductor devices, is an extremely important process for generating a pattern among semiconductor manufacturing processes. In recent years, with the high integration of LSI, circuit line widths required for semiconductor devices have been reduced year by year. In order to form a desired circuit pattern on these semiconductor devices, a highly accurate original pattern (also referred to as a reticle or a mask) is required. The electron beam drawing apparatus is used for producing such a high-precision original pattern.

FIG. 18 is a conceptual diagram for explaining the operation of the variable shaped electron beam drawing apparatus.
The variable shaped electron beam (EB) drawing apparatus operates as follows. In the first aperture 410, a rectangular opening 411 for forming the electron beam 330 is formed. Further, the second aperture 420 is formed with a variable shaping opening 421 for shaping the electron beam 330 having passed through the opening 411 of the first aperture 410 into a desired rectangular shape. The electron beam 330 irradiated from the charged particle source 430 and passed through the opening 411 of the first aperture 410 is deflected by the deflector, passes through a part of the variable shaping opening 421 of the second aperture 420, and passes through a predetermined range. The sample 340 mounted on a stage that continuously moves in one direction (for example, the X direction) is irradiated. That is, the drawing area of the sample 340 mounted on the stage in which the rectangular shape that can pass through both the opening 411 of the first aperture 410 and the variable shaping opening 421 of the second aperture 420 is continuously moved in the X direction. Drawn on. A method of creating an arbitrary shape by passing both the opening 411 of the first aperture 410 and the variable shaping opening 421 of the second aperture 420 is referred to as a variable shaping method (VSB method).

In electron beam drawing, with the miniaturization of integrated circuits, the shot size is reduced and the number of shots is increased. As a result, the drawing time becomes longer. Therefore, it is desired to shorten the drawing time, in other words, to improve the throughput of the drawing apparatus. In order to improve the throughput of the drawing apparatus, it is necessary to increase the current density of the electron beam. In order to increase the current density, it is necessary to increase the brightness of the cathode of the electron gun serving as the beam source. As the cathode, for example, lanthanum hexaboride (LaB ₆ ) crystal is used (see, for example, Patent Document 1). In order to increase the brightness of the thermionic emission cathode, there is a method of increasing the cathode temperature. However, increasing the cathode temperature increases the evaporation rate of the cathode material, thus shortening the cathode life. For example, in a cathode made of lanthanum hexaboride (LaB ₆ ) crystal, it is difficult to raise the cathode temperature significantly, for example, higher than 1800K. For this reason, there is a limit to achieving high brightness by raising the temperature of the cathode used.

On the other hand, in a LaB ₆ crystal manufactured by the zone melting method or the like, the composition ratio of lanthanum (La) and boron (B), the concentration of impurities, and the like differ depending on the position in the crystal. Therefore, even if a plurality of cathodes are manufactured from the same crystal lump, the brightness obtained by the completed cathodes varies. Therefore, even when a plurality of cathodes are manufactured, there is a problem that many cathodes that do not have a desired luminance when used in an electron beam apparatus are included.

JP 2005-228741 A

  Accordingly, an object of the present invention is to provide a technique for overcoming the above-described problems and selecting a cathode that can obtain a desired luminance.

The cathode sorting method of one embodiment of the present invention includes:
Measuring a total emission current emitted from the cathode using a cathode having a flat electron emission surface and a limited emission area;
Using the measured total emission current value to calculate the work function from the Richardson Dashman equation;
The desired luminance satisfying the Langmuir equation that defines the luminance using a term obtained by dividing the product of the current density J of the electron emission surface, the elementary charge e, and the acceleration voltage V by the product of the cathode temperature T and the Boltzmann constant k is Calculating the upper limit of the work function corresponding to the current density to be obtained;
Determining whether the work function is a cathode below the upper limit ;
It is provided with.

  The allowable value is preferably a work function value for obtaining a desired luminance that satisfies the Langmuir equation.

  Further, it is preferable to further include a step of measuring the emission area using an optical microscope.

  In addition, it is preferable to further include a step of measuring the temperature of the electron emission surface of the cathode at the time of electron emission from the cathode.

  The cathode temperature is preferably measured at a temperature within the temperature limited region.

  According to one embodiment of the present invention, a cathode that can obtain desired luminance can be selected. Therefore, a cathode corresponding to high luminance can be obtained.

FIG. 3 is a flowchart showing main steps of the cathode selection method in the first embodiment. 3 is a cross-sectional view illustrating an example of a cathode in Embodiment 1. FIG. FIG. 5 is a cross-sectional view showing another example of the cathode in the first embodiment. FIG. 5 is a cross-sectional view showing another example of the cathode in the first embodiment. 2 is a conceptual diagram illustrating an example of an electron emission surface of a cathode and a comparative example in Embodiment 1. FIG. 6 is a diagram illustrating an example of imaging an electron emission surface in the first embodiment with an optical microscope. FIG. 3 is a conceptual diagram illustrating a device configuration of a work function acquisition parameter measurement device according to Embodiment 1. FIG. 4 is a graph showing the relationship between total emission current and cathode temperature in the first embodiment. FIG. 3 is a conceptual diagram for explaining a temperature limiting region and a space charge region in the first embodiment. 2 is a graph showing an example of a measurement result of the total emission current and the cathode temperature in Embodiment 1 and a relationship thereof. 3 is a graph showing a relationship between a work function and a cathode temperature in the first embodiment. 4 is a graph showing an example of a measurement result of work function and cathode temperature in Embodiment 1 and a relationship thereof. 6 is a diagram illustrating an example of a relationship between luminance and work function in Embodiment 1. FIG. 4 is a diagram illustrating an example of a relationship between a ratio and work function in all cathodes in the first embodiment. FIG. FIG. 3 is a conceptual diagram showing a configuration of a drawing apparatus equipped with a selected cathode in the first embodiment. FIG. 10 is a conceptual diagram illustrating a device configuration of a work function acquisition parameter measurement device according to a second embodiment. FIG. 10 is a conceptual diagram illustrating a device configuration of a work function acquisition parameter measurement device according to a third embodiment. It is a conceptual diagram for demonstrating operation | movement of a variable shaping type | mold electron beam drawing apparatus.

For example, the luminance B of a thermionic emission type cathode using lanthanum hexaboride (LaB ₆ ) crystal is the current density J of the electron emission surface, the cathode temperature T, the Boltzmann constant k, the elementary charge e, and the acceleration voltage V. Can be defined by Langmuir's formula (1).

  Therefore, it can be seen that the current density J of the electron emission surface may be increased in order to increase the luminance. Further, the current density J of the electron emission surface in the equation (1) is defined by the following Richardson-Dashman equation (2) using the work function φ, the Richardson constant A, the cathode temperature T, and the Boltzmann constant k. it can.

The Richardson constant A is theoretically 120 A / cm ² K ² for a LaB ₆ crystal, for example, but in practice it has been found that about 80 A / cm ² K ² is appropriate. From equation (2), it can be seen that in order to increase the current density J of the electron emission surface, in other words, in order to increase the luminance, it is only necessary to reduce the work function φ. However, it is not easy to reduce the work function φ. Conventionally, there is no work function reduction method that can be applied to cathode manufacturing at a practical level. As described above, for example, in a LaB ₆ crystal manufactured by a zone melting method or the like, the composition ratio of lanthanum (La) and boron (B), the concentration of impurities, and the like vary depending on the position in the crystal. . Therefore, even if a plurality of cathodes are manufactured from the same crystal lump, the work function obtained by the completed cathode varies. Further, since the current density J of the electron emission surface can be defined as a value obtained by dividing the total emission current I by the area S of the electron emission surface, the work function φ can be expressed by the following Richardson by modifying equation (2). -It can be defined by equation (3), which is a dashman variant.

  Therefore, in the first embodiment, focusing on such work function variation, the cathode is selected based on the value of the work function.

  FIG. 1 is a flowchart showing main steps of the cathode selection method according to the first embodiment. In FIG. 1, the cathode selection method in the first embodiment includes a cathode manufacturing step (S102), an emission area measurement step (S104), an electron emission step (S106), a work function calculation step (S112), and an allowable value. A series of steps of a calculation step (S120), a determination step (S122), a selection step (S124), and a determination step (S126) are performed. Further, during the electron emission step (S106), a total emission current measurement step (S108) and a temperature measurement step (S110) are performed.

In the cathode manufacturing step (S102), first, a cathode to be selected is manufactured. The manufactured cathode is formed in a shape having a flat electron emission surface and a limited emission area. In other words, an emission area limited type cathode having a flat electron emission surface is manufactured. The cathode is manufactured by, for example, a mass of LaB ₆ crystals by a zone melting method or the like. Then, such a lump is processed to produce a plurality of cathodes. Here, the manufactured cathode may be formed from the same crystal or may be formed from different crystals.

FIG. 2 is a cross-sectional view showing an example of the cathode in the first embodiment. In FIG. 2, for example, the cathode 10 tapers the upper part of a cylindrical LaB ₆ crystal 20 into a tapered shape, and processes the upper surface 11 into a flat surface. For example, a carbon (carbon) film 30 is disposed on the entire tapered upper side surface. As will be described later, since the lower portion of the LaB ₆ crystal 20 is covered with a heater or the like, only the upper surface 11 formed on a flat surface is exposed when heated, and the exposed upper surface 11 is used as an electron emission surface. It can be limited to. Therefore, the electron emission area can be limited to the area S of the upper surface 11.

FIG. 3 is a cross-sectional view showing another example of the cathode in the first embodiment. In FIG. 3, the cathode 10 processes the upper surface 11 of a LaB ₆ crystal 21 having a hexagonal cross section into a flat surface. A carbon film 31 is disposed on the entire side surface. Even in such a configuration, only the upper surface 12 formed on a flat surface is exposed when heated, and the exposed upper surface 12 can be limited to the electron emission surface. Therefore, the electron emission area can be limited to the area S of the upper surface 12.

FIG. 4 is a cross-sectional view showing another example of the cathode in the first embodiment. In FIG. 4, the cathode 10 has a convex portion at the center of the upper portion of the LaB ₆ crystal 22, and a carbon film 32 is disposed on the entire surface other than the convex portion upper surface 13. The convex upper surface 13 is processed into a flat surface. Even in such a configuration, only the upper surface 13 formed on a flat surface is exposed when heated, and the exposed upper surface 13 can be limited to the electron emission surface. Therefore, the electron emission area can be limited to the area S of the upper surface 13.

FIG. 5 is a conceptual diagram showing an example of an electron emission surface of a cathode and a comparative example in the first embodiment. In Equation (3), in order to calculate the work function φ with high accuracy, it is necessary to measure the area S of the electron emission surface with high accuracy. As shown in FIG. 5A, in the cathode having a structure in which the exposed surface of the LaB ₆ crystal is not limited, the area of the electron emission surface changes depending on the cathode temperature and the Wehnelt voltage (bias voltage). Therefore, the work function φ cannot be obtained accurately. On the other hand, as shown in FIG. 5B, in the cathode having a structure in which the exposed surface of the LaB ₆ crystal is limited only to the upper surface of the plane, the electrons are not related to the cathode temperature and the Wehnelt voltage (bias voltage). It is emitted almost uniformly from the emission surface. Actually, since the electric field distribution on the emission surface is not completely uniform, the current density distribution may not be completely uniform. However, it has been experimentally known that if the total emission current and the emission area can be measured with high accuracy, it is possible to compare the effective work function φ with high accuracy.

  Therefore, in the first embodiment, as described above, the cathode 10 having a shape with a flat electron emission surface and a limited emission area is used.

  In the emission area measurement step (S104), the emission area of the upper surface 11 (12, 13) serving as the electron emission surface is measured for the plurality of manufactured cathodes using an optical microscope.

FIG. 6 is a diagram illustrating an example of the electron emission surface in the first embodiment imaged by an optical microscope. Carbon 30 is arranged around the LaB ₆ crystal 20 serving as an axis. The emission area S can be calculated by measuring the diameter or radius of the LaB ₆ crystal 20. Furthermore, since the upper surface is flat, the area can be calculated with high accuracy.

  In the electron emission step (S106), the parameters for obtaining the work function by emitting electrons from each of the manufactured cathodes are measured.

  FIG. 7 is a conceptual diagram showing a device configuration of the work function acquisition parameter measurement device according to the first embodiment. In FIG. 7, the measuring apparatus 300 includes a vacuum vessel 50, an electron gun power supply 60, and an ammeter 70. In the electron gun power supply 60, an acceleration voltage power supply 62, a Wehnelt power supply 64, and a heater power supply 66 are arranged. The cathode (−) side of the acceleration voltage power supply 62 is connected to the cathode 10 in the vacuum vessel 50. The anode (+) side of the acceleration voltage power supply 62 is connected to the anode electrode 54 in the vacuum vessel 50 and grounded. An ammeter 70 is connected in series between the anode (+) of the acceleration voltage power supply 62 and the anode electrode 54. The cathode (−) of the acceleration voltage power source 62 is also branched and connected to the anode (+) of the Wehnelt power source 64, and the cathode (−) of the Wehnelt power source 64 is connected between the cathode 10 and the anode electrode 54. Connected to Wehnelt 56. Further, in the vacuum vessel 50, the portion of the cathode 10 opposite to the electron emission surface that is not covered with the carbon film is covered with the heater 59. The heater power supply 66 is connected to the heater 59. The Wehnelt 56 is formed with an opening for allowing electrons emitted from the electron emission surface of the cathode 10 to pass to the anode electrode 54 side. The cathode 10 is heated by the heater 59 in a state where a constant negative Wenelt voltage (bias voltage) is applied to the Wenelt 56 from the Wenelt power source 64 and a constant negative acceleration voltage is applied to the cathode 10 from the acceleration voltage power source 62. Then, electrons (electron group) are emitted from the cathode 10, and the emitted electrons (electron group) are accelerated by the accelerating voltage to become an electron beam and travel toward the anode electrode 54. Here, the total emission current I is measured by changing the cathode temperature T in a state where the acceleration voltage and the Wehnelt voltage are set to constant values.

  In the total emission current measuring step (S108), the total emission current when the electron beam is emitted from the cathode 10 toward the anode electrode 54 is measured by the ammeter 70 using the measuring device 300. By measuring the current between the accelerating voltage power source 62, the cathode 10, the anode electrode 54, and the series circuit connected to the accelerating voltage power source 62 with the ammeter 70, the total emission current emitted from the cathode 10 can be measured. Measuring the current value of such a circuit with the ammeter 70 enables simpler and more accurate measurement than measuring the current of the electron beam itself with a detector such as a Faraday cup.

  As a temperature measurement step (S110), the temperature of the electron emission surface of the cathode 10 is measured when electrons are emitted from the cathode 10. The vacuum container 50 is provided with a window 58 (viewing port) that allows the inside to be directly viewed from the outside. The window 58 is preferably arranged at a position where the electron emission surface of the cathode 10 can be directly viewed. Thereby, the temperature of the electron emission surface at the time of electron emission can be measured. In the example of FIG. 7, an opening is formed on the side surface of the Wehnelt 56, and the electron emission surface of the cathode 10 can be directly viewed from the window 58 through the opening of the Wehnelt 56. A pyrometer 72 (temperature measuring device) is disposed in the vicinity of the window 58 outside the vacuum vessel 50. Thereby, the temperature of the electron emission surface of the cathode 10 is measured from the outside of the vacuum vessel 50 by the pyrometer 72. The cathode temperature is measured at a temperature within the temperature limited region.

  FIG. 8 is a graph showing the relationship between the total emission current and the cathode temperature in the first embodiment. The vertical axis represents the total electron emission current I, and the horizontal axis represents the cathode temperature T. When the current density J is replaced by the total emission current I and the area S of the electron emission surface and the Richardson Dashman equation (2) is transformed, the total emission current I is the following Richardson Dashman transformation equation. It can be defined by equation (4).

  In the cathode 10 having a certain work function φ, the area S of the electron emission surface is fixed. Therefore, when the cathode temperature T is increased, the total emission current I is calculated as shown in FIG. Increase according to Dashman's equation (4). However, when the cathode temperature T is further increased, the temperature limit region shifts to the space charge region, and the total emission current I becomes a constant value in the space charge region.

  FIG. 9 is a conceptual diagram for explaining the temperature limiting region and the space charge region in the first embodiment. When the cathode temperature is lower than a certain limit value, all the electrons emitted from the cathode 52 travel toward the anode electrode 54 as shown in FIG. In such a state, the number of electrons emitted is a function of the cathode temperature. That is, the Richardson Dashman equation is established. The cathode temperature region in this state is the temperature limiting region. On the other hand, when the cathode temperature rises and exceeds the limit value, the number of electrons emitted from the cathode 52 increases, and an electron cloud called a space charge 82 is formed on the front surface of the cathode 52. The space charge 82 has a negative feedback effect on the electron emission phenomenon from the cathode 52. In such a state, the number of electrons emitted does not depend on the cathode temperature. The cathode temperature region in such a state becomes a space charge region. In the first embodiment, the measurement is performed at the cathode temperature in the temperature limited region where the Richardson Dashman equation is established.

  FIG. 10 is a graph showing an example of the measurement result of the total emission current and the cathode temperature and the relationship thereof in the first embodiment. The vertical axis represents the total electron emission current I, and the horizontal axis represents the cathode temperature T. Here, an example of the result when the output of the acceleration voltage power source is set to 10 kV and the Wehnelt voltage is set to 0.5 kV is shown. As shown in FIG. 10, the total emission current I was measured when the cathode temperature T was changed to 1650K, 1700K, 1750K, 1800K, and 1850K. As a result, the total emission current I gradually increased and became a constant value after about 1750K. Therefore, the measurement result of the total emission current I at 1750K or less is used for the work function calculation.

  In the work function calculation step (S112), the work function is calculated from the Richardson Dashman equation using the measured value of the total emission current I. Here, the above-described equation (3) may be used.

  FIG. 11 is a graph showing the relationship between the work function and the cathode temperature in the first embodiment. The vertical axis represents the work function φ of the cathode, and the horizontal axis represents the cathode temperature T. By substituting the measured electron emission surface area S, cathode temperature T, and total emission current I into equation (3), which is a modified equation of Richardson Dashman, the work function φ of the cathode to be measured is calculated. That's fine. As shown in FIG. 11, the work function φ is constant within the range of measurement error in the temperature limited region. On the other hand, in the space charge region, the work function φ apparently rises as the cathode temperature rises because it does not follow the Richardson Dashman equation. Therefore, in the first embodiment, a constant value in the temperature limited region may be set as the work function φ of the cathode.

  FIG. 12 is a graph showing an example of the measurement result of the work function and the cathode temperature and the relationship thereof in the first embodiment. The vertical axis represents the work function φ of the cathode, and the horizontal axis represents the cathode temperature T. FIG. 12 shows an example of the work function φ calculated from the measurement result shown in FIG. As shown in FIG. 12, the work function φ when the cathode temperature T was varied to 1650K, 1700K, 1750K, 1800K, and 1850K was calculated. As a result, the work function φ showed a constant value in the error range, and started to increase after passing 1750K. Therefore, in Embodiment 1, the calculation result of the work function φ at 1750K or less is used.

  In the first embodiment, an average value of a plurality of calculation results of the work function φ in the temperature limited region is set as the value of the work function φ of the cathode. Thereby, the error can be reduced. However, the present invention is not limited to this, and if the error is within an allowable range, the value of the cathode work function φ calculated from the total emission current I at one cathode temperature in the temperature limited region may be used. .

  As an allowable value calculation step (S120), an allowable value φm of the work function φ for obtaining a desired luminance B is calculated. As the allowable value φm, a work function value for obtaining a desired luminance B satisfying Langmuir's formula (1) is used.

  FIG. 13 is a diagram illustrating an example of a relationship between luminance and work function in the first embodiment. In FIG. 13, the vertical axis represents the luminance B and the horizontal axis represents the work function φ. For example, a work function value satisfying Langmueller's formula (1) is calculated for a desired brightness B when used in an electron beam lithography apparatus or the like. By transforming the equation (2), the work function φ can be defined by the following equation (5), which is a modified equation of Richardson Dashman.

  On the other hand, the current density J can be defined by the following equation (6) by modifying the Langmuir equation (1).

By substituting equation (6) into equation (5), the upper limit of work function φ that satisfies luminance B according to Langmuir's equation (1) can be obtained. For example, when the luminance B is required to be 1.2 × 10 ⁶ A / cm ² sr or more, the upper limit of the work function φ is 2.628 eV. Therefore, the allowable value φm under such conditions is 2.628 eV.

  As a determination step (S122), it is determined whether or not the work function φ of the cathode to be measured is a small cathode having an allowable value φm or less.

  As a sorting step (S124), if the cathode as a result of the determination has a work function φ of the cathode to be measured is a permissible value φm or less, the cathode is selected as a usable cathode (ok). As a result of the determination, if the work function φ is larger than the allowable value φm, it is selected as an unusable cathode (NG).

  In the determination step (S126), it is determined whether all manufactured cathodes have been selected. If all the manufactured cathodes have not been selected, the process returns to the emission area measuring step (S104), and determination is made from the emission area measuring step (S104) until all manufactured cathodes are selected. The steps up to step (S126) are repeated. If all the manufactured cathodes have been selected, the process ends.

  Here, the emission area measurement step (S104), the electron emission step (S106), the work function calculation step (S112), the determination step (S122), and the selection step (S124) include all the manufactured cathodes. After each, the process may proceed to the next step.

  FIG. 14 is a diagram illustrating an example of the relationship between the ratio of work to all cathodes and the work function in the first embodiment. An example of the result of calculating the above-described work function for all manufactured cathodes is shown. As shown in FIG. 14, it can be seen that the work function value of the manufactured cathode varies as a characteristic. For example, it can be seen that the above-mentioned cathode having a work function φ of 2.628 eV or less is only a few percent of all manufactured cathodes. Therefore, even if a large number of cathodes are manufactured, the proportion of cathodes that can be used in an electron beam lithography apparatus that requires high brightness with the recent miniaturization of patterns is small. Therefore, it is necessary to select such a small number of cathodes efficiently. Therefore, the significance of sorting by the sorting method of Embodiment 1 is great.

  As described above, according to the first embodiment, it is possible to select a cathode that can obtain a desired luminance B. Therefore, a cathode corresponding to high luminance can be obtained.

  FIG. 15 is a conceptual diagram showing a configuration of a drawing apparatus equipped with a selected cathode in the first embodiment. Here, an electron beam drawing apparatus is shown as an example of an electron beam apparatus on which the selected cathode is mounted. In FIG. 15, the drawing apparatus 100 includes a drawing unit 150 and a control circuit 160. The drawing apparatus 100 is an example of an electron beam drawing apparatus. In particular, it is an example of a variable shaping type drawing apparatus. The drawing unit 150 includes an electron column 102 and a drawing chamber 103. In the electron column 102, there are an electron gun 201, an illumination lens 202, a first aperture 203, a projection lens 204, a deflector 205, a second aperture 206, an objective lens 207, a main deflector 208, and a sub deflector 209. Has been placed. An XY stage 105 is disposed in the drawing chamber 103. On the XY stage 105, a sample 101 such as a mask to be drawn at the time of drawing is arranged. The sample 101 includes an exposure mask for manufacturing a semiconductor device. Further, the sample 101 includes mask blanks to which a resist is applied and nothing is drawn yet. The selected cathode 10 in the first embodiment is mounted on the electron gun 201.

  The electron beam 200 emitted from the electron gun 201 (emission unit) illuminates the entire first aperture 203 having a rectangular hole by the illumination lens 202. Here, the electron beam 200 is first shaped into a rectangle. Then, the electron beam 200 of the first aperture image that has passed through the first aperture 203 is projected onto the second aperture 206 by the projection lens 204. The deflector 205 controls the deflection of the first aperture image on the second aperture 206, and can change (variably shape) the beam shape and dimensions. The electron beam 200 of the second aperture image that has passed through the second aperture 206 is focused by the objective lens 207, deflected by the main deflector 208 and the sub deflector 209, and continuously moved. The desired position of the sample 101 arranged in the above is irradiated. FIG. 1 shows a case in which multi-stage deflection of main and sub two stages is used for position deflection. In such a case, the electron beam 200 of the corresponding shot is deflected while following the stage movement to the reference position of the sub-field (SF) where the stripe region is further virtually divided by the main deflector 208. What is necessary is just to deflect the beam of the shot concerning each irradiation position.

  Since the selected high-intensity cathode is mounted, drawing processing can be performed with desired luminance.

Embodiment 2. FIG.
In the first embodiment, the window for measuring the temperature of the electron emission surface of the cathode from the side surface direction of the optical axis from the cathode to the anode is arranged, but the present invention is not limited to this. The contents other than those described in particular are the same as those in the first embodiment.

  FIG. 16 is a conceptual diagram showing a device configuration of the work function acquisition parameter measurement device according to the second embodiment. 16 is the same as FIG. 7 except that the arrangement position of the window 58 and a member that forms an opening for avoiding a shield between the window 58 and the electron emission surface of the cathode 10 are different. . In FIG. 16, the window 58 is disposed on the wall surface of the vacuum vessel 50 on the back side of the anode electrode 54. An opening is formed in the anode electrode 54, and the electron emission surface of the cathode 10 can be directly viewed from the window 58 through the opening of the anode electrode 54. A pyrometer 72 (temperature measuring device) is disposed in the vicinity of the window 58 outside the vacuum vessel 50. Thereby, the temperature of the electron emission surface of the cathode 10 is measured from the outside of the vacuum vessel 50 by the pyrometer 72.

  Even if configured as described above, the same effect as in the first embodiment can be exhibited.

Embodiment 3 FIG.
In the first and second embodiments, the configuration is such that only one cathode 10 can be disposed in the work function acquisition parameter measurement device 300, but this is not a limitation. In Embodiment 3, an example in which a plurality of cathodes are arranged simultaneously will be described. Hereinafter, the contents other than those specifically described are the same as those in the first or second embodiment.

  FIG. 17 is a conceptual diagram showing a device configuration of a work function acquisition parameter measurement device according to the third embodiment. In FIG. 17, measuring apparatus 300 according to Embodiment 3 simultaneously arranges a plurality of cathodes 10 in vacuum vessel 50. The Wehnelt 56 is arranged for each cathode 10. Further, the anode electrode 54 may be common. The electron gun power supply 60 and the ammeter 70 may be arranged for each cathode 10. An acceleration voltage power source (not shown) in the electron gun power source 60 and the cathode 10 are connected in parallel to the common anode electrode 54. An accelerating voltage power source (not shown) in the electron gun power source 60, the cathode 10, the anode electrode 54, and the current between the series circuits connected to the accelerating voltage power source are measured by the respective ammeters 70. The emission current I can be measured simultaneously. In the example shown in FIG. 17, each cathode temperature measurement window 58 is arranged on the wall surface of the vacuum vessel 50 on the back side of the anode electrode 54. Then, an opening is formed in each anode electrode 54 that shields between the corresponding window 58 and the cathode 10. A common pyrometer 72 (temperature measuring device) is arranged outside the vacuum vessel 50. Regarding the measurement of the cathode temperature, the temperature of the electron emission surface of the cathode 10 may be measured in order by the pyrometer 72 from the outside of the vacuum vessel 50 when the cathode 10 emits electrons by moving the common pyrometer 72.

The embodiments have been described above with reference to specific examples. However, the present invention is not limited to these specific examples. The electron beam apparatus on which the selected cathode is mounted is not limited to the drawing apparatus, and can be applied to other electron beam apparatuses such as an electron microscope. Further, as the cathode material has been described as an example LaB ₆ crystal, a tungsten (W), such as cerium hexaboride (CeB _6), it can be applied to other thermionic emission material. Further, although a carbon film is used to limit the electron emission surface of the cathode, it is not limited to carbon. In addition, any material such as rhenium (Re) having a higher work function than the electron emission material may be used.

  In addition, although descriptions are omitted for parts and the like that are not directly required for the description of the present invention, such as a device configuration and a control method, a required device configuration and a control method can be appropriately selected and used. For example, although the description of the control unit configuration for controlling the drawing apparatus 100 is omitted, it goes without saying that the required control unit configuration is appropriately selected and used.

  In addition, all cathode selection methods, cathode selection measuring devices, electron beam drawing apparatuses, and methods that include elements of the present invention and can be appropriately modified by those skilled in the art are included in the scope of the present invention.

10 Cathode 11, 12, 13 Upper surface 20, 21, 22 LaB ₆ Crystal 30, 31, 32 Carbon film 50 Vacuum vessel 54 Anode electrode 56 Wehnelt 58 Window 59 Heater 60 Electron gun power supply 62 Accelerating voltage power supply 64 Wehnelt power supply 66 For heater Power supply 70 Ammeter 100 Drawing apparatus 101, 340 Sample 102 Electron barrel 103 Drawing chamber 105 XY stage 150 Drawing unit 160 Control circuit 200 Electron beam 201 Electron gun 202 Illumination lenses 203, 410 First aperture 204 Projection lens 205 Deflector 206 , 420 Second aperture 207 Objective lens 208 Main deflector 209 Sub deflector 300 Measuring device 330 Electron beam 411 Opening 421 Variable shaped opening 430 Charged particle source

Claims (4)

Measuring a total emission current emitted from the cathode using a cathode having a flat electron emission surface and a limited emission area;
Using the measured total emission current value to calculate the work function from the Richardson Dashman equation;
The desired luminance satisfying the Langmuir equation that defines the luminance using a term obtained by dividing the product of the current density J of the electron emission surface, the elementary charge e, and the acceleration voltage V by the product of the cathode temperature T and the Boltzmann constant k is Calculating the upper limit of the work function corresponding to the current density to be obtained;
Determining whether the work function is a cathode below the upper limit ;
A cathode sorting method characterized by comprising: Cathode screening method according to claim 1, further comprising a step of measuring the emission area using an optical microscope. Wherein when the electron emission from the cathode, the cathode sorting method according to claim 1 or 2, further comprising a step of measuring the temperature of the electron emission surface of said cathode. The cathode selection method according to claim 3 , wherein the temperature of the cathode is measured at a temperature within a temperature limited region.

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